That's apparently because he'd been added to a sanctions list that Moscow issued in 2014, though his name did not appear on any lists made public at the time.

The US and Russia have been engaged in a tit for tat sanctioning individuals since 2012, when the US approved the so-called Magnitsky List, a collection of Russian individuals accused of human rights abuses. Since then, any new addition to the Magnistky List has resulted in Russia adding a complementary number of Americans to its own rolls.

The former ambassador was himself unaware of his ban until he attempted to travel to work on Hillary Clinton's potential transition to the White House in December.